Trump is doing something no candidate has done in almost 30 years, and it could pay off

But even more interesting than whom he picks may be when he picks. Trump has said several times that he won't reveal his choice until the Republican National Convention in July.

Traditionally, candidates have announced their running mates a week or two before their party's convention. Some wait just a few days before the big event, as John McCain did in 2008 when he chose Sarah Palin.

But if Trump keeps his word, it will be the first time in almost 30 years that a candidate has waited until the convention to reveal the person who will join him on the presidential ticket.

Only two candidates in modern history have waited until the convention to announce their picks: George H.W. Bush, when he tapped Dan Quayle in 1988; and Ronald Reagan in 1980, when he chose Bush.

The unconventional move is calculated on Trump's part, and it could pay major dividends for his campaign, said Richard Parker, a Harvard public-policy lecturer and former political consultant.

Trump "is a master of free media, and part of what he's going to do with the VP nomination is the free-media strategy," Parker told Business Insider. "The media will hunger and hunger and hunger for the name of the VP candidate, and the surge will build in a crescendo of interest in who he appoints."

Chip Somodevilla/Getty Images

"I think that he's following the strategy logically with how he's run the campaign to this day," he added.

Trump said earlier this month that he had narrowed his vice-presidential short list to "four or five politicians from within the party's establishment," including some of his former rivals from the Republican primary.

But as the convention draws near, the real question is who will want the job.

"There's going to be a real examination by a lot of Republicans whether they want to associate with him," Parker told Business Insider.